PURPOSE: To determine if form-deprived aphakes, like normal infants, show especially poor sensitivity in the nasal visual field. The purpose of this article was also to examine the influence on their peripheral sensitivity of the timing and duration of deprivation, of whether deprivation was monocular or binocular, and of having patched the fellow nondeprived eye. METHODS: Static perimetry was used to measure intensity thresholds at 20 degrees in the nasal visual field and at 30 degrees in the temporal visual field in normal subjects (n = 20 7-year-old children, 20 8-year-old children, 12 9-year-old children, and 20 adults) and in 46 children treated for a dense and central cataract in one (n = 21) or both (n = 25) eyes. The deprivation began either at birth or after a normal early history, and the duration of deprivation varied widely among patients. Also tested were two adults who had been treated promptly for unilateral cataracts that had developed after the age of 40 years. RESULTS: In normal subjects, sensitivity was slightly higher at 20 degrees nasally than at 30 degrees temporally, with no developmental changes in sensitivity at either location. The deprived eyes of the children had losses in sensitivity at both locations but only children treated for unilateral congenital cataract had larger losses at 20 degrees nasally than at 30 degrees temporally. There were no significant effects on their sensitivity of the duration of deprivation or, in children treated for unilateral cataract, of patching of the nondeprived eye. In contrast, the two patients in whom cataracts did not develop until adulthood had normal sensitivity. CONCLUSIONS: Pattern deprivation interferes with the development of peripheral sensitivity at both 30 degrees temporally and 20 degrees nasally. Nasal sensitivity, which is slow to mature, is affected more by early monocular deprivation than by early binocular deprivation. The results are consistent with the hypothesis that unfair interocular competition during early infancy especially affects visual functions that are slow to mature.